The present invention relates to a method and a device for detecting pinholes on hermetically sealed packages, which wrap, with an electric insulating film, conductive contents, e.g, medical consumable products such as blood products and normal saline solutions, as well as foods, etc.
Hermetically sealed packages are used in a variety of products today to maintain the sterilized condition of the contents of these products. These products include a number of products, for example, a variety of medical consumable products such as blood for transfusion and blood products, as well as food products such as retort foods.
It is extremely important to inspect these hermetically sealed packages for pinholes. A pinhole in the package of a medical consumable product causes contamination or decomposition of the contents. A pinhole in the package of a food product causes the contents to contact the atmosphere, leading to decomposition or decay of the contents.
In a conventional method for detecting pinholes, for example, that described in Japanese (Examined) Patent Application Publication S50-6998 (1975), a subject, which is a packaged item, is placed between a pair of electrodes. When a voltage is applied to these electrodes while substantially differentiating the electrostatic capacity formed between one electrode and the subject and the electrostatic capacity formed between the other electrode and the subject, a spark is produced between one electrode and the subject, causing an electric current. The existence of a pinhole can be detected when the electric current is detected.
In the above method, in which the existence of a pinhole is detected by detecting the electric current caused by the spark, the existence of a pinhole is actually detected by the variation in the strength of the detected current (whether it becomes stronger or weaker).
In this case, when a voltage is applied to the two electrodes that hold a hermetically sealed package between them, either a leakage current or a charging current always flows regardless of the existence of a pinhole. Such a current becomes stronger as the voltage becomes higher. The current is also affected by the climate, for example, the humidity and temperature of the periphery of the subject, which form the atmosphere at the time of the inspection. The leakage current, for example, becomes stronger when it rains or when the humidity is high. Fine floating dust also affects the electric current at the detector. When checking the existence of a pinhole by the magnitude of the electric current running in a short period of time, the detector sometimes concludes that there is a pinhole even if there is no pinhole. In this method, malfunctions are inevitable.
Moreover, when a high voltage is applied to the two electrodes holding a hermetically sealed package between them, an electric potential difference concentrates on the weak portion of the electric insulating film of the hermetically sealed package, providing a cause for pinholes. As a result, there will be more pinholes, adversely affecting the subject.
In order to solve these problems, the applicant invented a method (Japanese Pat. No. 2908751, etc.) in which a hermetically sealed package is installed on a supporting electrode that is grounded, a high direct current voltage is applied between the supporting electrode and yet another electrode that contacts or approaches the test portion of the hermetically sealed package in close proximity, and the electrode that contacts the test portion is grounded while the ground of the supporting electrode is disengaged or kept engaged, thereby detecting a discharge current from the test portion to inspect the hermetically sealed package for pinholes.
According to this method, the existence of a pinhole on a hermetically sealed package can be checked efficiently, but the method still requires a series of inspection procedure. In a further exploration for an easier procedure, the applicant developed a technology that does not require the supporting electrode that contacts the side surface of the hermetically sealed package (Japanese Patent Application H10-211868 (1998), Japanese Patent Application H11-16597 (1999)).
In this method, an electrode is placed so as to contact or approach the test portion of the hermetically sealed package in close proximity, and a high voltage is applied between the test portion of the hermetically sealed package and the supporting electrode that supports the hermetically sealed package. In the previously mentioned method in which the existence of a pinhole is detected by detecting the current generated by a spark, a high voltage is applied between the electrodes that hold the hermetically sealed package. In either method, while it is possible to check whether or not there are pinholes on the surface of the test portion of the hermetically sealed package that the supporting electrode contacts, it is impossible to check whether or not there are pinholes on the two, relatively wide, opposing surfaces of the hermetically sealed package in simultaneous inspections of the both surfaces.
During the course of further explorations and experiments for a better method of inspection that replaces the above method, the applicant discovered that when a high voltage is applied to a hermetically sealed package having relatively flat surfaces through its two opposing surfaces, it is possible to check whether or not there are pinholes on at least one of the relatively flat opposing surfaces of the hermetically sealed package in simultaneous inspections from the both surfaces. This discovery has led to the present invention.
The present invention is extremely effective when it is applied to hermetically sealed packages having flat surfaces, in particular, those containing such contents as medical consumable products including blood products, e.g., blood for transfusion, plasma, etc., as well as foods, etc., including retort foods. The present invention can also be applied to packages that do not have flat surfaces, for example, those having circular arc surfaces, as long as the conductive elements of the present invention can contact relatively wide areas of the exterior circular arc surfaces.
According to the inspection method of the present invention, while a hermetically sealed package 3, which wraps, with an electric insulating film 2, conductive contents 1, e.g., blood for transfusion, blood products, etc., is conveyed, a conductive element 5 arranged on one side of the package""s path A and at least one of the two longitudinally arranged conductive elements 6, 6 arranged on the other side are made to simultaneously contact the opposing surfaces of the contents 1xe2x80x94existing portion of the hermetically sealed package 3. In this condition, a high voltage is applied to the hermetically sealed package 3 to detect a change in the electric current at the portion where the conductive element 5 contacts or the portion where at least one of the two conductive elements 6, 6 contacts, thereby detecting a pinhole on the hermetically sealed package 3.
Using this method, the conductive element 5 arranged on one side of the path A and at least one of the two longitudinally arranged conductive elements 6, 6 arranged on the other side contact the portions of the opposing surfaces of the contents 1xe2x80x94existing portion of the hermetically sealed package 3. In this condition, a high voltage is applied to the hermetically sealed package 3 to detect a change in the electric current at the portion where the conductive element 5 contacts or the portion where at least one of the two conductive elements 6, 6 contacts, thereby checking the existence of a pinhole on at least one of the portions on the opposing surfaces of the contents 1xe2x80x94existing portion of the hermetically sealed package 3 in simultaneous inspections of both surfaces.
According to the inspection device of the present invention, two conveyors 4, 4 for conveying the hermetically sealed package 3, which wraps, with an electric insulating film 2, conductive contents 1, e.g., blood for transfusion, blood products, etc., are arranged longitudinally with an interval between them that is sufficiently small for the hermetically sealed package 3 to be handed over from one to the other. The conductive element 5 approaches the path A from one side of the space between the two conveyors 4,4 and the two conductive elements 6, 6 approach the path A from the other side of the path A. At this time, these conductive elements are longitudinally separated from each other for such distances that make it possible for the conductive element 5 and at least one of the two conductive elements 6, 6 to contact the opposing surfaces of the contents 1xe2x80x94existing portion of the hermetically sealed package 3 from both sides of the path A simultaneously as the package is conveyed. A high-tension power unit 7 is connected to either the conductive element 5 or the two longitudinally arrange conductive elements 6,6, which approach the path A from each respective side. An electric current detector 8 for detecting an electric current change at the portion where the conductive element 5 contacts and the portion where at least one of the two longitudinally arranged conductive elements 6,6 contacts is connected to the other.
Using this device, the hermetically sealed package 3 can be conveyed by the operation of the two longitudinally conveyors 4, 4. From both sides of the path A, the conductive element 5 arranged on one side of the path A and at least one of the two longitudinally arranged conductive elements 6, 6 arranged on the other side, simultaneously contact the opposing surfaces of the contents 1xe2x80x94existing portion of the hermetically sealed package 3 that is moving on the path A. In this condition, a high voltage is applied to the hermetically sealed package 3 from the high-tension power unit 7. If a change in the electric current is detected by the electric current detector 8 at the portion where the conductive element 5 contacts and the portion where at least one of the two longitudinally arranged conductive elements 6, 6 contacts, it is concluded that at least one of the opposing surfaces of the contents 1xe2x80x94existing portion of the hermetically sealed package 3 has a pinhole. In this way, it is possible to inspect the entire areas of the opposing surfaces of the contents 1xe2x80x94existing portion of a hermetically sealed package 3 simultaneously from both surfaces to check whether or not there is a pinhole on any portion of at least one of the opposing surfaces.
Specifically, in the condition in which the conductive element 5 arranged on one side of the path A and at least one of the two longitudinally arranged conductive elements 6, 6 arranged on the other side simultaneously contact the opposing surfaces of the contents 1xe2x80x94existing portion of the hermetically sealed package 3 being conveyed from both sides of the path A, a high voltage is applied to the hermetically sealed package 3 to check by the electric current detector 8 whether there is a change in the electric current at the portion where the conductive element 5 contacts and the portion where at least one of the two longitudinally arranged conductive elements 6,6 contacts.
If there is a pinhole on any portion of at least one of the opposing surfaces of the contents 1xe2x80x94existing portion of the hermetically sealed package 3 being conveyed, over the entire areas of the opposing surfaces, a change occurs in the electric current at the portion where the conductive element 5 contacts and the portion where at least one of the two longitudinally arranged conductive elements 6, 6 contacts. If the electric current detector 8 detects the change in the electric current, it is concluded that at least one of the opposing surfaces of the contents 1xe2x80x94existing portion of the hermetically sealed package 3 has a pinhole. In this way, it is possible to inspect the entire areas of the opposing surfaces of the contents 1xe2x80x94existing portion of a hermetically sealed package 3 simultaneously form both surfaces to check whether or not there is a pinhole on any portion of at least one of the opposing surfaces.
On the other hand, if there are no pinholes on any portion of the entire areas of the opposing surfaces of the contents 1xe2x80x94containing portion of the hermetically sealed package 3 being conveyed, no change occurs at the portion where the conductive element 5 contacts and the portion where at least one of the two longitudinally arranged conductive elements 6, 6 contacts, therefore, the electric current detector 8 does not detect any change in the electric current. In this way, it is possible to inspect the entire areas of the opposing surfaces of the contents 1xe2x80x94existing portion of the a hermetically sealed package 3 simultaneously from both surfaces to check whether or not there is a pinhole on any portion of at least one of the opposing surfaces.
In the present invention, the longitudinal distance between the two conductive elements 6, 6, which are on the opposite side of the path A from the conductive element 5, can be extended generously within the range in which either one of them and the conductive element 5 can simultaneously touch the opposing surfaces of the contents 1xe2x80x94existing portion of the hermetically sealed package 3 being carried. Accordingly, the conductive element 6 and the conductive element 5 can be separated as far as possible. As a result, it is possible to make it difficult to produce sparks between the conductive element 6 and the conductive element 5, raising the limit to which the applicable voltage can be increased without causing any problem to inspections for pinholes.
The inspection method described in claim 1 has the following advantages: it makes it possible to check whether there is a pinhole on at least one of the opposing surfaces of the contents-existing portion of a hermetically sealed package in simultaneous inspections of both surfaces; and it also makes it possible to increase the voltage applied.
The inspection device of the present invention has the following effect: it is possible to convey relatively flat hermetically sealed packages one after another, and while doing so, inspect the entire areas of the opposing surfaces of the contents 1xe2x80x94existing portion of a hermetically sealed package 3 simultaneously from both surfaces to check continuously, accurately and without an error whether or not there is a pinhole on any portion of at least one of the opposing surfaces.